CD48^−/− HSCs show a defect in both short-term and long-term activity. (A) Donor chimerism in the peripheral blood measured with CD45.2 expression, from transplants of 100 000 donor WBM cells competed against 100 000 WT WBM cells. CD48^−/− HSCs show a substantial transplantation defect (nonlinear regression analysis, P = .02061). (B) Lineage contribution of CD48^−/− HSCs at 12 weeks. CD48^−/− recipients show a slight but insignificant skewing toward the T-cell lineage at the cost of B cells. (C) Donor chimerism in the peripheral blood measured with CD45.2 expression, from competitive transplants of 300 000 WBM cells from either a CD48^−/− mouse or WT mouse. CD48^−/− HSCs still exhibit a substantial transplantation defect (nonlinear regression analysis, P < .01) at the higher BM dose. (D) Noncompetitive BM transplant with 300 000 CD48^−/− or WT whole BM cells. Shown is the proportion of peripheral blood (CD45.1⁺) cells generated from the donor cells at the indicated time points (all error bars are SEM).